i just downloaded some brushes and the extension .ABR is this the othing you extract into photoshop? < sorry noobie question.
If you have Photoshop open when you put the .abr files into your Brushes folder (in the Presets folder), you'll have to restart PS.
Another possiblility is to import manually then you don't have to restart it. But i guess restart is quicker...
if I am using a set of brushes, I just replace the current ones or add them to the bottom, no need for me to restart
You can also choose to put all your brushes in a seperate folder, and then replace them with the ones you want.